1. Field of the Invention
The present invention relates to an oil pump having a sealing mechanism for a pumping chamber.
2. Background of the Related Art
A conventional oil pump, as shown in FIG. 5, is disclosed in Japanese Utility Model Laid-open No. 61(1986)-179385. An inner rotor 100 and an outer rotor 101 are rotatably supported in a housing 102 and have lobes which mesh with each other. A shaft 105 drives the rotor 100, and the rotor 101 via the rotor 101. Revolution centers of the rotors 100 and 101 are different from each other so that spaces 110 of varying volumes are formed therebetween. One of the spaces 110 which starts to communicate with suction port 103 has the smallest volume, and each of the succeeding spaces 110 in the direction of rotation of the rotors becomes larger in volume. When each of the spaces 110 is located at a position where the respective space 110 is in communication with neither the suction port 103 nor a discharge port 104, the volume of the respective spaces 110 becomes largest. The space having the largest volume is designated by numeral 111. After that, each of the spaces 110 becomes smaller in volume during further revolution of the rotors 100 and 101.
A pocket 120 is formed in the housing 102 and is located opposite to the space 111. The pocket 120 communicates with the discharge port 104 via a passage 121 which is also formed in the housing 102.
Oil pressure in the space 111 is high and pushes the inner rotor 100 inwardly and the outer rotor 101 outwardly. However, the pressure in the pocket 120, which communicates with the discharge port 104 via the passage 121, pushes the outer rotor 101 inwardly. Thus the gap between the rotors 100 and 101 which is generated by the pressure in the space 111 is controlled to a minimum and the leakage of oil through the gap into suction port 103 via the spaces 110 communicating with the suction port 103 is controlled.
The pocket 120 and the passage 121 accordingly act as a sealing mechanism for the space 111. However, forming such a passage 121 within the housing is complicated.